how to solve unhandled exception error when using visual C++ 2008?

Question

Hi,

Could someone please help me to solve unhandled exception error when using visual C++ 2008? the error is displayed as follow: Unhandled exception at 0x00411690 in time.exe: 0xC0000005: Access violation reading location 0x00000008

Some details:
- tm 0x00000000 {tm_sec=??? tm_min=??? tm_hour=??? ...} tm *
tm_sec CXX0030: Error: expression cannot be evaluated
...

Actually when I used visual c++ 6 in the past, there weren't any error and the program was running fine. But now ehen I use visual 2008, I am getting this Unhandled exception error.

Here is the program:

...
int gettimeofday(struct timeval *tv, struct timezone *tz)
{
  FILETIME ft;
  unsigned __int64 tmpres = 0;
  static int tzflag = 0;

  if (NULL != tv)
  {
    GetSystemTimeAsFileTime(&ft);

    tmpres |= ft.dwHighDateTime;
    tmpres <<= 32;
    tmpres |= ft.dwLowDateTime;

    tmpres /= 10;  /*convert into microseconds*/
    /*converting file time to unix epoch*/
    tmpres -= DELTA_EPOCH_IN_MICROSECS; 
    tv->tv_sec = (long)(tmpres / 1000000UL);
    tv->tv_usec = (long)(tmpres % 1000000UL);
  }

  if (NULL != tz)
  {
    if (!tzflag)
    {
      _tzset();
      tzflag++;
    }
    tz->tz_minuteswest = _timezone / 60;
    tz->tz_dsttime = _daylight;
  }

  return 0;
}


uint32_t stampstart()
{
 struct timeval  tv;
 struct timezone tz;
 struct tm      *tm;
 uint32_t         start;

 gettimeofday(&tv, &tz);
 tm = localtime(&tv.tv_sec);

 printf("TIMESTAMP-START\t  %d:%02d:%02d:%d (~%d ms)\n", tm->tm_hour,
        tm->tm_min, tm->tm_sec, tv.tv_usec,
        tm->tm_hour * 3600 * 1000 + tm->tm_min * 60 * 1000 +
        tm->tm_sec * 1000 + tv.tv_usec / 1000);   /////---debugger stops here---

 start = tm->tm_hour * 3600 * 1000 + tm->tm_min * 60 * 1000 +
  tm->tm_sec * 1000 + tv.tv_usec / 1000;

 return (start);

}

thanks for your replies:

Answer 1

With that address, my SWAG is that tm is NULL. Since you never check for the NULL after the call to localtime(), you are dereferencing a NULL pointer.

Edit: SWAG = Scientific Wild Ass Guess.

The address 0x00000008 is the same offset of tm.tm_hour. You are trying to access tm->tm_hour when you pass in the parameter to printf().

Answer 2

The access violation refers address 0x00000008, which probably means that your code is accessing a field at offset 8 in a struct to which you point with a NULL pointer. I guess that localtime returns a NULL pointer. Check this.

Answer 3

"Access violation reading location 0x00000008"

An address that low is probably caused by accessing a null pointer. In this case, tm is probably 0 because of a problem with localtime or gettimeofday. You get address 0x08 instead of 0x00 because the compiler is trying to read a value 8 bytes into the struct.

Answer 4

Try Something like...

 tm = localtime(&tv.tv_sec);
if(tm)
{
 printf("TIMESTAMP-START\t  %d:%02d:%02d:%d (~%d ms)\n", tm->tm_hour,
        tm->tm_min, tm->tm_sec, tv.tv_usec,
        tm->tm_hour * 3600 * 1000 + tm->tm_min * 60 * 1000 +
        tm->tm_sec * 1000 + tv.tv_usec / 1000); 

 start = tm->tm_hour * 3600 * 1000 + tm->tm_min * 60 * 1000 +
  tm->tm_sec * 1000 + tv.tv_usec / 1000;
}
else
{
 // failed to retrive local time
}

Answer 5

The type of member tv.tv_sec is long, but localtime expects a time_t * parameter. In VC6 this worked because both long and time_t were 32-bit, but in VS2008 time_t is a 64-bit type so they are incompatible.

This should fix it:

//add to beginning of stampstart function:
time_t t;

//... other code...

//put this instead of call to localtime:
t = tv.tv_sec;
tm = localtime(&t);